This study is designed to investigate the influence of various factors, such as antibiotic resistance, genetic characteristics, host immune response, on the incidence and pathogenicity of Pseudomonas aeruginosa in a cancer patient population. A monovalent lipopolysaccharide fraction of type 2 P. aeruginosa is used as an immunogen in C3H female adult mice. Agglutinin and antigen-coating immunoglobulin levels and the class of Ig in the mouse sera were determined. The importance of these antibodies in the control of P. aeruginosa infection is an ongoing study. The kinetics of the antibody response and its regulation will be performed by the modified Jerne plaque method. In vitro susceptibilities of Pseudomonas spp. other than P. aeruginosa to certain antibiotics have changed significantly from the antibiograms of these species in an earlier study.